1. Field of the Invention
The present invention relates to a gas insulating switchgear, and more particularly, to a gas insulating switchgear which does not require a high insulating strength of a vacuum interrupter within a switchgear while satisfying a whole insulating strength required for the switchgear. More specifically, the present invention relates to a gas insulating switchgear which is capable of reducing a production cost compared to that of a conventional art and of performing installation of a cable towards a power supply or a cable towards a load to be connected with an apparatus of the present invention and its maintenance work under the safe circumstance.
2. Description of the Background Art
Generally, the electricity is generated at about 20,000V in an electric power station, boosted to an ultra-high voltage to be suitable for power transmission and then transmitted to a first substation. Upon receipt of the ultra-high voltage, the first substation drops it to 22.9 KV and supplies it to a second substation or to each customer.
The power supplied from the first substation to the second substation or to each customer is supplied to a power receiving facility of each customer through a distributing system having a terrestrial distribution line or a subterranean distribution line, and supplied to an ultra-high voltage consumer and a high voltage consumer and also supplied even to a low voltage consumer through various outdoor installed transformer.
In order to identify and branch the subterranean distribution lines and protect a first coil of the transformer, a gas insulating switchgear, so called a ring main unit, is used.
For the gas insulating switchgear, a SF6 gas insulating switchgear using SF6 gas as an insulating material is widely used, which includes a manually operated switchgear and a remotely operated switchgear in terms of its operating methods.
For example, a conventional gas insulating switchgear uses a vacuum interrupter which extinguishes arc generated when a switch is on or off by using vacuum having a comparatively good insulating strength.
In case that the arc extinguishing of the switchgear using the vacuum interrupter is applied to a switchgear having a rated insulation breakage voltage of 125 KV, since the arc extinguishing and insulation between contact points are fulfilled within the vacuum interrupter, the rated voltage level of the vacuum interrupter should be more than 125 KV, accordingly.
However, the vacuum interrupter becomes expensive as its rated insulation breakage voltage is higher. Thus, in case of employing a vacuum interrupter of a higher rated insulation breakage voltage, the overall production cost of the switchgear us dependently increased.
In addition, a switching means of the convention switchgear is the only vacuum interrupter having only two switching positions including switch on or switch off, so that, when the cable is installed, maintained and repaired, the switchgear itself is not able to perform ground function of a cable.
Moreover, when the switch is off (the circuit is opened), the distance between a movable contact and a fixed contact is about 10xcx9c20 mm. In this respect, in case that a high voltage is generated between the movable contact and the fixed contact (that is, in case that arc is generated), the security of a worker is degraded.
Therefore, an object of the present invention is to provide a gas insulating switchgear which is capable of satisfying a required high rated insulation breakage while not raising the rated insulation breakage level of a vacuum interupter, to thereby reduce a production cost.
Another object of the present invention is to provide a gas insulating switchgear which is capable of grounding a high-voltage current in the case where a cable towards a power-source or a load is installed, maintained and repaired, to thereby ensure a safe working.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a glass insulating switchgear including: a first switching means for connecting or breaking an electric circuit between a power source and a load; a second switching means being mechanically and electrically connected with the first switching means and being selectively movable to an electrically conducting position, an electrically breaking position or an electrically grounding position; and an actuator being connected for supplying a driving force to the second switching means so that the second switching means can be moved.